The invention relates to a tacheometer telescope according to the precharacterizing clause of claim 1. Such a telescope system is disclosed in the patent application of the present Applicant, submitted to the German Patent Office on 2.9.1998.
Tacheometers are defined as theodolites with integrated distance meters. For distance measurement, either a reflector is mounted on the target object (cooperative target object) and sighted either manually or with the aid of automatic target recognition or a natural target object without such target marking (noncooperative target object) is sighted manually. In spite of the rapid development of electrooptical distance meters (EDM) during the past twenty years, however, very few tacheometers measuring without reflectors are commercially available today. Where there was a need for these, virtually all apparatuses measuring without reflectors and developed for the geodetics sector were in fact realized as add-on distance meters for technical reasons, such add-on instruments being mounted on the respective theodolites by means of a mechanical or electromechanical adapter.
As a result of the design according to the above-mentioned patent application submitted on 2.9.1998, both cooperative and noncooperative target objects can be recognized. It is true that tacheometers having integrated electrooptical distance meters measuring without reflectors are already known per se (ZEISS REC Eita-RL). Such apparatuses are also used both for surveying cooperative target objects and for measuring distances to objects having natural rough surfaces, for example for surveying poorly accessible surfaces, as in quarries, tunnel profiles, road profiles, building facades, etc.
Distance meters measuring without reflectors are as a rule based on the principle of measurement of the transit time of an emitted optical radiation pulse. Compact apparatuses with economical energy consumption always use a pulsed laser diode with a peak output power of about 1 watt to more than 100 watt. In these apparatuses, pulsed infrared semiconductor laser diodes having large emitting surfaces are used as a radiation source. A disadvantage arises from the relatively large dimensions of the emitting surfaces of these lasers, of the order of magnitude of 100 xcexcm or more. This results in a radiation slope of this apparatus of about 1.5 mrad or more, with the result that a beam cross-section of as much as 15 cm is present at a distance of 100 m. Distances to structures which are smaller than 15 cm therefore cannot be measured. The physical reason for the large beam diameter is that the radiation sources used to date emit non-diffraction-limited radiation. On the other hand, one disadvantage of a radiation beam having a large cross-section is that, in the case of measurements to inclined or structured surfaces of the objects, it is not the true distance which is measured but a distance value intensity-weighted over the irradiated area, and hence the result of the measurement is falsified.
Another disadvantage of electrooptical distance meters measuring without reflectors is that, owing to the infrared or extensive measuring radiation, the object point actually sighted is not detectable. However, in order nevertheless to visualize the target location, it is necessary to use an additional beam, in particular a laser beam, with visible and diffraction-limited emission, whose beam axis must also be adjusted relative to the transmitted beam axis.
In addition to all these difficulties, it is also generally necessary, apart from the distance between the points, also to determine associated angles with geodetic accuracy, and to do so in a distance range from 0.1 m to about 2000 m or more. In general, it is desired to implement surveying tasks as ergonomically as possible. To meet this requirement, it was necessary to date to mark target points with reflection-supported means. Such cooperative target points can be sighted, for example, very rapidly by automatic target recognition (ATR) and surveyed using the conventional infrared distance meter. However, it is not always possible to mount a reflection-supporting means on the target object. Owing to obstacles which cannot be overcome, such as building heights, rivers, lack of authorization for access to plots, etc., certain target objects are not accessible and therefore cannot be marked by reflection means. Consequently, both target points having a natural surface and those which reflect have to be sighted in one and the same surveying task. This was not possible at all using known tacheometers. Apart from the disadvantage of not being able to provide simultaneously in a single instrument all sensors necessary in geodetic surveying tasks, which in any case complicates the surveying task, existing electronic theodolites have the additional deficiency of not complying with the required accuracy of measurement of 1 mm, in particular in distance measurement without reflectors.
A further complicating factor is a desirable miniaturization of a theodolite, i.e. housing a plurality of measuring components in a very small space. This is because even the theodolites equipped with few sensors, in particular theodolite telescopes, which are available at present have relatively large outer dimensions and are therefore heavy, impeding ergonomic use in the field. These are tacheometers with automatic target recognition (ATR) or theodolites having only one EDM measuring to targets without reflectors. In the past, this was certainly one of the reasons why no attempt was made to completely equip a single theodolite, and, where necessary, different measuring tasks were performed using different instruments. It is particularly difficult to miniaturize telescopes of those theodolites which are to have automatic target recognition, since the accuracy of measurement required in geodetic applications is typically 3 to 5 cc (=8 xcexcrad) or 1 mm point resolution. Such accuracies are achievable only with long focal distances, which, in spite of additional optical components, results in a great constructional length of the optical system. However, shortening may impair the accuracy of angular measurement, in particular if the automatic target recognition is performed by means of a separate, for example biaxial, beam path separated from the visual channel (PCT-SE90-00233).
It is therefore the object of the invention to provide a telescope for an electronicxe2x80x94in particular motorized, preferably with respect to both axesxe2x80x94theodolite, by means of which the geodetic needs can be better covered. In particular, it is the object of the present invention, in addition to a visual telescope and a distance meter measuring only to reflecting target objects, for example an infrared distance meter, to design a diffraction-limited, reflectorless distance meter together with a miniaturized sensor unit for automatic target point recognition and to integrate it in a theodolite telescope.
The telescope equipped with sensors should have as small outer dimensions as possible in order to meet the requirements for convenience during field measurements. Furthermore, the energy consumption should be so low that battery operation is at least possible.
The special challenge of the object according to the invention is in particular to nest four optical channels of 4 independent sensors in one another in such a way that their function individually and in mutual cooperation is ensured. On the one hand, a sensor must operate satisfactorily by itself; on the other hand, the channels may not interfere with one another when functioning simultaneously.
According to the invention, the extension of the object for a telescope according to the precharacterizing clause of claim 1 is possible through the characterizing features of this Claim. This permits not only distance measurement to cooperative and noncooperative target objects but additionally angle determination, in particular cases alternatively with manual or automatic sighting. Thus, natural objects, such as rocks or trees, and buildings, church steeples and other towers can be measured as target objects to be surveyed, as well as targets supported by a reflector, such as a retroprism, reflecting foil, retroreflector or the like. The optical target axis is an excellent direction firstly for the angle measurement relative to the horizontal reference axis, for example in the north direction, and/or relative to the vertical reference axis, for example the vertical axis of the theodolite, which are determined with the aid of separate angle sensors, and secondly for the measurement of the residual angle between target object and target axis, which is performed by means of automatic target recognition with image evaluation and angle calculation. Of course, it may also be possible to use other position-sensitive sensors. However, an advantage of image-generating sensors is the possibility of image documentation.
There is in principle already a large number of applications for a reflectorless method of measurement. Thus, it is sufficiently well known that distances up to 100 m on rough surfaces can be measured without additional marks, such as reflectors or reflective marks. For a required accuracy of measurement of 1 to 3 mm, the divergence of the transmitted beam must be as small as possible since otherwise the distance measurement would not give the required accuracy, owing to the undefined target object illumination. The same applies to the divergence of the received beam. A small divergence reduces the proportion of the simultaneously received ambient light, so that the signal/noise ratio in the receiver is advantageously influenced. On the other hand, a small divergence in a fixed focus arrangement does however have the disadvantage that the overlap of transmitted and received beams is small close up. This is at least alleviated by the coaxial arrangement of transmission and receiving optical systems. To achieve the accuracy of measurement of 1 mm, however, additional technical measures are required, which are to be discussed below.
However, while the classical surveying method in land surveying, building surveying or industrial surveying consists in recording and staking out points with known and unknown coordinates in the object space or on the target object, according to the invention all this is performed using a single instrument. After all, the erection of an instrument (positioning and orienting) takes a certain time, which it is intended to reduce by carrying out all measurements using a single instrument. However, simply the erection and setting up of an instrument according to the invention results in the advantage that, for example when setting up a measuring station with poorly accessible connection points, this task can be performed in one operation by means of reflectorless distance measurement. On the other hand, other points which are marked by prisms or reflective marks can be efficiently measured with the same setup and with the same instrument, and the measurements are performed by means of automatic target recognition, which saves time and additionally increases the accuracy of measurement.
For practical reasons, it is advantageous for the purposes of the invention if the telescope additionally has a visual channel, in particular to an eyepiece, apart from a respective optical transmission and receiving channel. This is because it is not always possible to mark the target point by reflection-enhancing or other means and to sight said target point by automatic target recognition. There are situations where it is possible only with particular effort, if at all, to find the target point automatically. Such target objects without special markings can thus be sighted visually or manually and the distance can then be determined by means of the distance measuring method to a natural target object without target marking, i.e. advantageously using diffraction-limited radiation of, for example, about 30 arc-seconds beam divergence, in particular emitting in the visible wavelength range. Particularly suitable for such reflectorless measurements are applications involving buildings, such as exterior facades or interior rooms. Particularly when used in an interior room, a visible measuring spot has the further advantage that target objects can be sighted directly by means of the visible measuring spot, such as a laser point, without looking through the telescope.
A further advantage of a visible measuring spot arises in the case of motor-controlled profile recordings, in particular of interior rooms. A motorized theodolite is in fact capable of scanning a predetermined profile and recording the corresponding polar coordinates on the measured object with the reflectorless distance meter. However, interruption of the measuring beam between the instrument and the target object by objects or persons is not a rare event. In such a case, a measurement is made to the obstacle which leads to distance measurements falsified in an undesired manner. In the case of the apparatus according to the invention, however, the reflectorless measuring beam is expediently chosen so that it is visible to the naked eye. Sightings to interfering obstacles are therefore immediately visible and can be easily corrected.
A further advantage arises from the cooperation of visible beams, in particular measuring without reflectors, with automatic target recognition. A visible beam, e.g. a laser beam, can in fact also be used as a laser pointer, as already mentioned. In particular, the measuring spot is readily visible to the naked eye even on reflection-supported target objects. Consequently, any error in the automatic target recognition is also easily visible and correctable.